The present invention relates to an optical integrated unit, an optical pickup, and an optical recording medium drive device. More specifically, the present invention relates to a flat-package type of optical integrated unit incorporating an integrated laser source for a plurality of operating wavelengths, such as those for DVD-ROM and CD-R disks, for reading signals recorded on an optical recording medium such as an optical disk and writing thereto, and also to an optical pickup using that optical integrated unit and an optical recording medium drive device using that optical pickup.
Digital versatile disk (DVD) systems are being developed for recording large volumes of data within a compact and also portable recording medium. When it comes to implementing such a system, it is preferable to provide compatibility that can also reproduce from disks of prior-art formats, such as compact disk, read-only memory (CD-ROM) and compact disk recordable (CD-R).
A semiconductor laser diode (herein after abbreviated to LD) of a wavelength of approximately 780 nm is used for readout from a CD-R, but an LD of a wavelength of 650 nm is used for DVD, for implementing a recording density of approximately seven times that of a CD-ROM. However, the recording medium used for CD-R is a pigmentation material and it is not possible to obtain sufficient sensitivity therewith in the 650-nm wavelength band used for DVDs. That is why it is essential to use an optical pickup that has two light sources, for implementing a DVD system that is compatible with CDs.
A schematic view of the configuration of a conventional two-light-source type of optical pickup for DVD is shown in FIG. 14. In this figure, reference number 101 denotes a 650-nm-wavelength optical integrated unit for DVD readout, 102 denotes a 780-nm-wavelength optical integrated unit for CD-R and CD-ROM readout, 103 denotes a prism, 104 denotes a collimator lens, 115 denotes a folding mirror, 106 denotes a wavelength selection filter, 107 denotes a focusing lens, 108 denotes a CD-format disk, and 109 denotes a DVD-format disk.
Each of the optical integrated units 101 and 102 is provided with a semiconductor laser that acts as a light source, alight-receiving element for detecting a light beam reflected from a disk, and a monitoring light-receiving element for controlling the output of the semiconductor laser.
An optical pickup that uses two independent light sources, such as that shown in FIG. 14, has problems as described below. The first problem relates to the complexity of adjusting the positions of the light sources because there are two optical axes, and the second problem is it is difficult to make the complete assembly smaller and lighter.
In order to solve these two problems, the present inventor and others have developed a integrated semiconductor laser element in which 650-nm and 780-nm light sources are integrated in a monolithic fashion on the same semiconductor substrate, which is designed to greatly simplify optical systems that use such a laser element. This was disclosed as Japanese Patent Application No. 10-181068.
A schematic view of a section through the structure of the integrated semiconductor laser element proposed by the present inventor and others in this application is shown in FIG. 15.
A perspective view in FIG. 16 shows essential components of an optical integrated unit in which an integrated semiconductor laser element is mounted in a CAN-type package, and a schematic view of the optical system of an optical pickup that uses this optical integrated unit is shown in FIG. 17.
As shown in FIG. 15, an integrated semiconductor laser element 31 has a 650-nm laser excitation portion 240 and a 780-nm laser excitation portion 241, formed in a monolithic manner on a common GaAs substrate 210. Respective p-side electrodes 233 and 234 of these laser excitation portions are attached by an adhesive material 351, such as an AuSn solder, on top of extraction electrodes 352 and 353 formed separately on top of an insulating substrate 354 of a material such as AlN. Reference number 358 denotes a metal block for heat dissipation.
In the optical integrated unit shown in FIG. 16, reference number denotes the previously mentioned integrated semiconductor laser element, 354 denotes an AlN insulating substrate, 358 denotes the metal block for heat dissipation, 359 denotes a photodiode (PD) for monitoring, and 360 denotes a divided PD for error detection and RF signal detection. These components are disposed on a stem 400 and are connected as appropriate by lead pins 404 and wires W through feed-throughs 402.
Components in FIG. 17 that are the same as those in FIG. 14 are denoted by the same reference numbers and further description thereof is omitted. In FIG. 17, reference number 361 denotes the optical integrated unit of FIG. 16 mounted in a CAN-type package.
It is clear that the optical system shown in FIG. 17 has a far simpler structure than that of the original optical system exemplified in FIG. 14, as a result of using a single optical integrated unit, so it can be made smaller and lighter.
However, there are still some technical problems to be solved with both the CAN-type optical integrated unit of FIG. 16 and the optical pickup of FIG. 17.
The first problem concerns the necessity of a high level of precision in the mounting of the LD 31 (in the X-Z plane) on a surface that is perpendicular to the mounting of the divided PD 360 (in the X-Y plane).
The second problem is that lead pins 361p, the metal block 358 for heat dissipation, the integrated semiconductor laser element 31, and IC chips (not shown in the figure) are disposed in a three-dimensional structure, which imposes a limit on the miniaturization of the assembly.
Concerning the first technical problem: the angle (xcex1) between the LD beam and the Z-axis is required to be within xc2x11xc2x0, the deviation in relative position (in the X-Y plane)between the luminous spot generated by the LD and the divided PD 360 is required to be within xc2x15 xcexcm, and the deviation (xcex2) between the angles of rotation of the LD 31 and the divided PD 360 is required to be within xc2x10.5xc2x0.
Concerning the second technical problem: this presents an obstacle to mounting the assembly in a notebook computer or personal data assistant (PDA) having an external thickness of 30 mm or less.
The present invention was devised in the light of the above described problems. In other words, an objective thereof is to provide a multi-wavelength optical integrated unit, optical pickup, and optical recording medium drive device which can be made much smaller, lighter, and slimmer than in the prior art, with a reduced number of components, reduced fabrication costs, and, simultaneously, an increased reliability.
In order to achieve this objective, an optical integrated unit in accordance with the present invention comprises a substrate and a semiconductor laser element mounted on a main surface of the substrate; wherein:
the semiconductor laser element has a configuration such that a first laser excitation portion for emitting a laser beam of a first wavelength and a second laser excitation portion for emitting a laser beam of a second wavelength that differs from the first wavelength are integrated in a monolithic manner, and also the laser beam of the first wavelength and the second laser beam are emitted in a substantially parallel direction with respect to the main surface of the substrate;
the substrate comprises:
a mirror surface inclined with respect to the main surface in such a manner that the first and second laser beams are reflected substantially perpendicularly upward with respect to the main surface; and
means for providing electrical separation between a first mount portion corresponding to the first laser excitation portion and a second mount portion corresponding to the second laser excitation portion.
In this case, the means for separation could be a p-n junction formed on a front surface of the substrate.
An optical pickup in accordance with the present invention comprises the previously described optical integrated unit and an optical system which focuses the laser beam of the first wavelength and the second laser beam that are emitted from the optical integrated unit to illuminate an optical recording medium therewith, and also guides light reflected back from the optical recording medium into the optical integrated unit.
An optical recording medium drive device in accordance with the present invention is characterized in having the above described optical pickup incorporated therein.
The present invention as implemented above has the effects described below.
First of all, the present invention makes it possible to create an optical integrated unit in which a semiconductor laser array integrated of semiconductor lasers of different lasing wavelengths is mounted on top of a substrate, which can emit light beams of a plurality of wavelengths by reflecting them upward by a mirror, and detect light returned thereto.
The use of such an optical integrated unit makes it possible to implement an optical pickup which has a greatly reduced number of components and which is smaller, lighter, and more reliable with a greatly simplified optical system.
More specifically, the present invention enables a single optical axis adjustment because the same optical axis is used for each wavelength of the optical pickup. It is also not necessary to use any two-wavelength creation means such as a dichroic prism. In addition, it is sufficient to use one each of components such as the laser element and holographic element, so it is not necessary to assemble other components such as signal detector PDs and monitor PDs.
In other words, the present invention has the huge production advantage of enabling the implementation of an optical disk drive device that incorporates an optical integrated unit which is far smaller and lighter than in the prior art and which is also highly reliable with respect to mechanical vibration and shock.